1. Field of the Invention
The invention relates to a composition for joint compound including recycled wallboard constituents and a method and system for making the same.
2. Description of the Related Art
Interior walls of commercial and residential dwellings, including manufactured housing, are typically made by mounting wallboard panels onto an existing stud structure with conventional fasteners such as nails or drywall screws. A pair of abutting panels often has an uneven seam which is filled with "joint compound," a filler which dries and hardens. The hardened joint compound is typically sanded to create a smooth and aesthetically pleasing wall surface which completes the drywall process. Joint compounds can be classified into two basic formulations, i.e., "setting" and "drying." The drying type of joint compound is often formulated as a ready-mixed joint compound, while the setting type is provided as a powder which typically requires the addition of water immediately prior to application.
The setting and drying types of joint compounds have varying characteristics. The drying type is often a combination based on limestone (CaCO.sub.3), gypsum (hemihydrate) (CaSO.sub.4 *1/2H.sub.2 O) and/or gypsum (dihydrate) (CaSO.sub.4 *2H.sub.2 O) while the setting type is often based on gypsum (hemihydrate) (CaSO.sub.4 *1/2H.sub.2 O). After application into and over a seam between a pair of adjacent wallboard panels, the drying type joint compound dries by contact with air via the ensuent evaporation of water while the setting type reacts chemically to harden within a predetermined time.
Manufacture of either type of joint compound is costly. The basic ingredients of joint compounds are expensive process. In addition, government regulations often require that various ingredients such as asbestos, mica and talc be added or removed from these formulations to increase their safety.
In construction today, about one and one half pounds of wallboard waste is generated per square foot of a constructed dwelling. In the case of manufactured housing, this number may increase to two or three pounds of wallboard waste per square foot. This waste is costly due to the cost of materials as well as the cost required to dispose of the waste wallboard.
The latter is a significant problem. After disposal, the wallboard may degrade under certain conditions to form dangerous by-products, such as hydrogen sulfide gas. In addition, the sheer volume of wallboard waste as well as the dangerous by-products formed during its degradation has led many municipal landfills to prohibit dumping of wallboard waste and to demand recycling programs.